1. Field of the Invention
This invention relates generally to improvements in a method and apparatus for the production of three-dimensional objects. Specifically the invention employs an inert or non-reactive support liquid on top of which is floated a reactive liquid medium. Sequential thin cross-sectional layers of the object are solidified by a source of synergistic stimulation selectively impinging upon the surface of the reactive liquid medium.
2. Description of the Prior Art
A variety of techniques have been proposed for producing three dimensional objects by selectively transforming reactive liquid media into solids. Good descriptions of a number of these processes may be found in Marshall Burns' booked entitled: "Automated Fabrication: Improving Productivity in Manufacturing and Rapid Prototyping & Manufacturing", PTR Prentice Hall, Englewood Cliffs, N.J., 1993. In a number of instances, the methods described therein are based upon solidifying a thin layer of material located at the surface of a reservoir containing a partially fabricated part submerged below the surface by an amount equal to the desired layer thickness. By repeating the following steps an object can be built up from a series of appropriately soldified thin cross-sections:
(1) forming a thin layer of desired thickness using a reactive liquid medium on the surface of a previously solidified layer or suitable supporting structure in the case of the first layer; and PA1 (2) selectively solidifying regions of the reactive liquid medium to a defined depth (i.e. thickness) corresponding to elements of the object's cross-section at that particular height position.
With respect to step (2), a variety of techniques have been proposed for solidifying the reactive liquid medium (hereafter referred to as "imaging"): translating an optical fiber in a plane parallel to the reactive liquid medium's surface, mask(s), as well as using a scanning system to position a laser beam on the liquid's surface to "draw" the cross-section of interest. Masking techniques for forming images include, but are not limited to, methods for forming masks out of line such as film, laser "writing" on special LCD substrates an example of which is described by Holian (S. K. Holian et al., "A New Method for Direct Imaging", Printed Circuit Fabrication, Vol. 12, No. 1, January 1989) or electrophotographic processes such as those disclosed in U.S. Pat. No. 4,961,154 (Pomerantz et al.), as well as programmable mask technologies examples of which include electro-luminescent displays, plasma displays, liquid crystal displays and micromirror arrays (U.S. Pat. No. 5,247,180--Mitcham et al.).
Rapid prototyping systems requiring the partially fabricated object to be substantially surrounded by reactive liquid medium for substantially the duration of the object fabrication process have a number of undesirable features: Production of even a very small part requires an entire reservoir to be filled with reactive liquid medium. This is especially troublesome when users need to make parts from different materials since one is forced to purchase a full reservoir of every material of interest which can prove to be very expensive. Material shelf life can become a problem if large quantities of reactive liquid medium are not routinely consumed. Production of large parts from a reservoir filled with a reactive liquid medium presents a number of problems: The cost of the reactive liquid medium alone would preclude very large parts such as a full scale car body model from being produced as a single piece. Environmental and worker safety considerations would also make handling of such large quantities of reactive liquid medium difficult. Part distortion resulting from absorption of reactive liquid medium during fabrication can pose problems since the object is surrounded by unreacted liquid medium for an extended period of time. Even if an object could be initially fully cured, the absorbed reactive liquid medium would require a post-cure step.
A number of prior art patents utilize inert liquids in conjunction with reactive liquid media in the context of producing three dimensional objects. U.S. Pat. Nos. 4,575,330 (Hull), 4,929,402 (Hull), 5,015,424 (Smalley), and 5,174,943 (Hull) all disclose a process in which a reactive liquid medium floats on the surface of an inert transparent liquid. Unlike the process of the present invention, however, these patents describe a process involving irradiation through the supporting liquid. The fabricated object is drawn away from the support liquid's surface. In this instance, the support liquid acts as a release agent. Without it, the newly formed layer would contact a solid surface and would be very difficult to remove. In the depicted embodiment, the inert fluid does not provide any support to the solidified layers as they are translated away from the imaging plane. Consequently thin overhanging layers would be difficult to form using this process.
U.S. Pat. No. 5,011,635 (Murphy et al.) also employs a second liquid phase. In this instance, however, a flexible membrane separates a volume containing the fabricated object and reactive liquid medium from the second liquid phase. Separating the phases with a membrane not only proves cumbersome from a practical standpoint but also fails to realize many of the benefits of true support fluid technology as discussed in the present disclosure.
Although some reduction in reactive liquid medium is realized by using the process disclosed in U.S. Pat. No. 5,011,635, the present invention offers an even greater reduction. In addition, unlike the present invention, this prior art process requires that the object be fully immersed in reactive liquid medium during the entire part fabrication cycle which can lead to object distortion. Other advantages of the present invention relative to this process will be apparent to the reader.
U.S. Pat. No. 5,120,476 (Scholz) involves polymerizing a fine stream that is sprayed onto the surface of a support liquid which is very different than selectively polymerizing regions of a thin film of photoresin floated on the surface of another liquid proposed in the present invention. Among other things, U.S. Pat. No. 5,120,476 does not employ a continuous photoresin layer, has a variable focal plane, and requires uninterrupted irradiation of the photopolymer.
U.S. Pat. No. 4,961,154 describes a rapid prototyping apparatus which employs a support material. Unlike the present invention, the support material may be a very high density material.
It was in light of the prior art as just described that the present invention was conceived and now has been reduced to practice.